Patent GB-541658-A (GB)
Title: Improvements in traffic control systems
IPC: G08G1/08
Filed: 1940-06-03
Abstract: 541,658. Road signals for controlling traffic. AUTOMATIC TELEPHONE & ELECTRIC CO., Ltd., PREIST, T. P., and THOMPSON. G. W. June 3, 1940, No. 9662. [Class 118 (ii)] In a vehicle-actuated system particularly for use at wide intersections, an all-red period is introduced when necessary in order to clear the traffic crossing the inter-section before right of way is transferred to another phase, the duration of the all-red period being continuously variable according to the conditions obtaining when the demand is received from the halted phase. The controller described is of the common camshaft type disclosed in Specification 512,439 and provides for a maximum of four phases. Demands on the various phases are dealt with in cyclic order, but modifications may be made as disclosed in Specification 533,449 to enable them' to be dealt with on a first-come first-served basis. When the controller is switched into service, the camshaft goes to position 2 in which relay CM pulls up. Assuming a demand on phase A, relay AR (operating over an ordinary or unidirectional detector DA, UDA) connects up ST, AP, APR, PT. The condenser timer QA is pre-charged, so that the camshaft advances at once to position 3, in which the amber period is timed by QC, and thence to position 1 in which AS, ASR operate, giving R.O.W. to phase A. Relays CM, ST, PT fall back, and AR is unlocked and connected in parallel with extension relay EX. The vehicle interval period and minimum green period are timed simultaneously by QA, QC, but only the latter controls the advance of the camshaft to the vehicle extension position 2. If a demand has been registered on phase B, say, BP, BPR (not shown) energize in place of AP, APR when this position is reached, AS, ASR remaining held, and connect up PT, whereupon, provided there have been no extensions on phase A, QA discharges through relay A and the camshaft goes to the amber and all-red position 3. Relay RR is operative in positions 1 and 2, and if an all-red period is provided after phase A, RC operates over strapped terminals TA 13, 14, followed by RZ. If the all-red period is unconditional, terminal TA 17 is strapped to TA 18 to hold RR in position 3, but if, for example, it is inserted after phase A only when R.O.W. is transferred to phase B or C, TA 17 is strapped to TA 20, 21, and the holding circuit is dependent on the operation of BPR or CPR (not shown). In the present instance, since RZ remains up, amber is shown only to phase A when the camshaft goes to position 3, and the timer QC controls RX and brings about the operation of RY, which unlocks, AS, ASR and sets up the all-red condition. Relays RR, RC, RZ relapse and CM re-operates, connecting RT in parallel with RY. The all-red period is timed by QD, and RX brings about the release of RT, RY, whereupon amber is shown to phase B. The camshaft goes to position 1 to give R.O.W. to phase B after the amber period has been timed. In the case described above, the full all-red period is inserted in the transfer from phase A to phase B. If when phase A receives R.O.W. there are no extensions and no demands, the vehicle interval timer QA operates SF and hence SX. The camshaft goes to position 2 on the expiry of the minimum green period, and an extension on phase A now releases SX and starts the timing of a fresh vehicle interval period which results in reoperation of SX, and the timer QD is connected up to time a clearance period. If a demand occurs on phase B during this period, the timer QD is disconnected by ST and remains partly charged so that when it is connected up to time the all-red period the latter is reduced by the portion of the clearance period which has already elapsed. To ensure that QA is fully charged to advance the camshaft immediately a demand occurs, SX connects a pre-charged condenser QE in parallel therewith. If no demand occurs until after the clearance period has elapsed, the all-red period is suppressed. The transfer may then take place in the normal manner or consecutive amber control may be employed. In the former case, the dotted line connection across contact rt 5, Fig. 2, is provided so that D operates at the end of the clearance period and connects up SZ which opens the holding circuit of RR in position 3. In the latter case, the sequence of operations is same as when an all-red period is inserted except that the duration of that period is reduced to zero since operation of D immediately follows that of RT. If however an extension occurs on phase A during the amber leaving period, QD is discharged by EX and a full all-red period ensues. Consecutive amber control may be provided at an intersection without the provision of all-red periods by means of strappings such as TA 13, 15 to permit operation of RZ without that of RC, so that no circuit is made for RY. A detector ARED that is connected to EX when RT is up may be provided to extend the all-red period when necessary, and QB is then used as an all-red maximum timer. Facilities are provided for manual operation by a push-button connected to terminal MPB, and a switch such as ASA associated with each phase when actuated simulates a demand on that phase. Specification 515,860, [Group XL], also is referred to.